Use of carboethoxysulfenyl chloride for disulfide bond formation

The use of carboethoxysulfenyl chloride for disulfide bond formation and concomitant cyclization of five peptides was investigated. Even though cyclic peptides were obtained very rapidly and in good yields when cyclization was performed in aqueous media at different pHs (4 to 7), the final crude peptides were found to contain closely related impurities which, in the case of somatostatin and pressinoic acid, were not generated by air oxidation. This observation may limit the use of carboethoxysulfenyl chloride to those cases where other methods of disulfide bond formation prove inadequate.